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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>, Jan Kara <jack@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jiri Slaby <jslaby@suse.com>, Andreas Mohr <andi@lisas.de>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: printk: what is going on with additional newlines?
Date: Tue, 29 Aug 2017 10:00:15 -0700	[thread overview]
Message-ID: <CA+55aFwmwdY_mMqdEyFPpRhCKRyeqj=+aCqe5nN108v8ELFvPw@mail.gmail.com> (raw)
In-Reply-To: <20170829134048.GA437@jagdpanzerIV.localdomain>

On Tue, Aug 29, 2017 at 6:40 AM, Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:
> Pavel reported that
>         printk("foo"); printk("bar");
>
> now does not produce a single continuation "foobar" line, but
> instead produces two lines
>                 foo
>                 bar

And that's the *correct* behavior.

Stop trying to fix that. Fix the printk's instead.

In particular, the

    printk("bar");

could have come from an interrupt, and have nothing what-so-ever to do
with "foo".

If you want continuations, you

 (a) make sure the first one doesn't end in a newline

 (b) make sure the second printk has a KERN_CONT

 (c) even after that, ask yourself how much you _really_ want
continuations, because there are going to be situations where it still
doesn't work.

I refuse to help those things. We mis-designed things, and the
continuations were a mistake to begin with, but they were a mistake
that was understandable in the timeframe they happened. But it's not
something we should support, and it's most definitely is not something
we should then say "oh, you were broken shit that didn't even bother
to add the KERN_CONT, let me help your crap".

No.

Only acceptable use of continuations is basically boot-time testing,
when you do things like

     printk("Testing feature XYZ..");
     this_may_blow_up_because_of_hw_bugs();
     printk(KERN_CONT " ... ok\n");

and anything else you should seriously try to marshal the data
*before* doing a printk(), and not expect printk() to marshal it for
you. But for legacy reasons, we do end up trying to support KERN_CONT.
Just barely.

I'd really like to get rid of it entirely, because the whole log-based
structure really really doesn't work well for it (what if somebody has
already read the partial line from the logs?)

Our printk stuff didn't used to be log-based. It was just a plain
character-based circular buffer. Back then that KERN_CONT made a whole
lot more sense.

              Linus

  parent reply	other threads:[~2017-08-29 17:00 UTC|newest]

Thread overview: 94+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-15  2:56 [RFC][PATCHv5 00/13] printk: introduce printing kernel thread Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 01/13] printk: move printk_pending out of per-cpu Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 02/13] printk: introduce printing kernel thread Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 03/13] printk: add sync printk_emergency API Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 04/13] printk: add enforce_emergency parameter Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 05/13] printk: enable printk offloading Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 06/13] printk: register PM notifier Sergey Senozhatsky
2017-08-15 11:51   ` Rafael J. Wysocki
2017-08-16  7:31     ` Sergey Senozhatsky
2017-08-16 12:58       ` Rafael J. Wysocki
2017-08-17  5:55         ` Sergey Senozhatsky
2017-08-17 15:43           ` Rafael J. Wysocki
2017-08-17 23:19             ` Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 07/13] printk: register syscore notifier Sergey Senozhatsky
2017-08-15 11:56   ` Rafael J. Wysocki
2017-08-16  6:55     ` Sergey Senozhatsky
2017-08-16 12:59       ` Rafael J. Wysocki
2017-08-15  2:56 ` [RFC][PATCHv5 08/13] printk: set watchdog_thresh as maximum value for atomic_print_limit Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 09/13] printk: add auto-emergency enforcement mechanism Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 10/13] printk: force printk_kthread to offload printing Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 11/13] printk: always offload printing from user-space processes Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 12/13] printk: do not cond_resched() when we can offload Sergey Senozhatsky
2017-08-15  2:56 ` [RFC][PATCHv5 13/13] printk: move offloading logic to per-cpu Sergey Senozhatsky
2017-08-23  8:33 ` [RFC][PATCHv5 00/13] printk: introduce printing kernel thread Sergey Senozhatsky
2017-08-28  9:05 ` printk: what is going on with additional newlines? Pavel Machek
2017-08-28 10:28   ` Sergey Senozhatsky
2017-08-28 12:21     ` Sergey Senozhatsky
2017-08-28 12:38       ` Sergey Senozhatsky
2017-08-28 12:46       ` Pavel Machek
2017-08-29 13:40         ` Sergey Senozhatsky
2017-08-29 16:37           ` Joe Perches
2017-08-29 17:00           ` Linus Torvalds [this message]
2017-08-29 17:12             ` Linus Torvalds
2017-08-29 20:41               ` Tetsuo Handa
2017-08-29 20:51                 ` Linus Torvalds
2017-09-02  6:12                   ` Tetsuo Handa
2017-09-02 17:06                     ` Linus Torvalds
2017-08-29 23:50               ` Steven Rostedt
2017-08-29 23:59                 ` Linus Torvalds
2017-08-30  1:03                 ` Sergey Senozhatsky
2017-08-30  1:10                   ` Steven Rostedt
2017-08-30  1:51                     ` Sergey Senozhatsky
2017-08-30  1:52                     ` Joe Perches
2017-08-30  2:25                       ` Sergey Senozhatsky
2017-08-30  2:31                         ` Joe Perches
2017-08-30  2:47                           ` Sergey Senozhatsky
2017-08-30  2:58                             ` Joe Perches
2017-08-30  5:37                               ` Sergey Senozhatsky
2017-09-08 10:18                                 ` Pavel Machek
2017-09-05  9:44                             ` Petr Mladek
2017-09-05  9:59                               ` Sergey Senozhatsky
2017-09-05 12:21                                 ` Petr Mladek
2017-09-05 12:35                                   ` Tetsuo Handa
2017-09-05 14:18                                     ` Sergey Senozhatsky
2017-09-05 13:42                                   ` Sergey Senozhatsky
2017-09-06  7:55                                     ` Petr Mladek
2017-09-17  6:26                                       ` Sergey Senozhatsky
2017-09-17  9:27                                         ` Sergey Senozhatsky
2017-09-17 15:35                                         ` Linus Torvalds
2017-09-18  0:46                                           ` Sergey Senozhatsky
2017-09-18  2:22                                             ` Joe Perches
2017-09-18  2:41                                               ` Sergey Senozhatsky
2017-09-18  2:45                                                 ` Joe Perches
2017-09-18  2:55                                                   ` Sergey Senozhatsky
2017-09-18  3:07                                                     ` Joe Perches
2017-09-18  4:42                                                       ` Sergey Senozhatsky
2017-09-01 13:19                     ` Sergey Senozhatsky
2017-09-01 17:32                       ` Joe Perches
2017-09-01 20:21                         ` Linus Torvalds
2017-09-04  5:22                           ` Sergey Senozhatsky
2017-09-04  5:41                             ` Joe Perches
2017-09-05 14:54                             ` Steven Rostedt
2017-09-06  2:14                               ` Sergey Senozhatsky
2017-09-06  2:36                               ` Linus Torvalds
2017-09-04  4:30                         ` Sergey Senozhatsky
2017-09-04  5:24                           ` Sergey Senozhatsky
2017-08-29 17:33             ` Sergey Senozhatsky
2017-08-29 17:52               ` Linus Torvalds
2017-08-29 18:09                 ` Joe Perches
2017-08-30  1:07                   ` Sergey Senozhatsky
2017-08-30  0:58                 ` Sergey Senozhatsky
2017-08-29 16:48   ` Linus Torvalds
2017-08-29 17:10     ` Joe Perches
2017-08-29 17:20       ` Linus Torvalds
2017-08-29 17:33         ` Joe Perches
2017-08-29 17:36           ` Linus Torvalds
2017-08-29 17:48             ` Joe Perches
2017-08-29 20:24     ` Pavel Machek
2017-09-01  1:40       ` Sergey Senozhatsky
2017-09-01  2:04         ` Joe Perches
2017-09-01  6:59           ` Pavel Machek
2017-09-01  7:23             ` Joe Perches
2017-09-01  7:29         ` Pavel Machek
2017-09-01 11:13           ` Steven Rostedt

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